1. Field of the Invention
This invention relates to reflector antennas. More particularly, the invention relates to a dual polarized reflector antenna assembly with signal path and Ortho Mode Transducer (OMT) configurations providing improved electrical performance.
2. Description of Related Art
Dual polarized microwave communications links utilize a pair of signals, each using different polarities, thus enabling a significant link capacity increase compared to single signal/dual polarity communications links. However, electrical performance with respect to each signal may be reduced, due to signal separation requirements and/or interference between each of the signals. With the increasing demand for link capacity in terrestrial communications systems, especially in limited RF spectrum environments, the use of dual polarized communications links is increasing.
Traditional terrestrial communications reflector antennas for use with single signal/dual polarity communications links may be provided in a compact assembly where the transceiver is mounted proximate the backside of the reflector dish. Thereby, the return loss requirement of the antenna may be relaxed, the insertion loss and link budget improved.
Due to the additional signal paths and function duplication to enable dual signal processing, typical dual polarization communications links utilize a reflector antenna with remote transceiver mounting, thus requiring additional waveguide plumbing and/or transceiver mounting requirements.
Dual polarized electrical signals received by the reflector antenna are separated by an OMT inserted into the signal path. The separated signals are then each routed to a dedicated transceiver.
Electrical performance considerations for dual polarized reflector antenna assemblies include the inter-port isolation (IPI) between the antenna feed and the two orthogonal polarization ports at the transceivers. The IPI performance of an OMT contributes to the cross polar discrimination (XPD) property of the overall antenna assembly. If the XPD of a dual polarized antenna assembly is degraded, the cross-polar interference cancellation (XPIC) will be poor, which means that the orthogonal channels will interfere with each other, degrading the overall communications link performance. However, if the OMT/signal paths are physically large, depolarization becomes an additional factor, as the signal energy has to travel an increased distance between the radio port and the feed port.
International patent application publications WO 2007/088183 and WO 2007/088184 disclose OMT and interconnecting waveguide elements, respectively, that together may be utilized in a dual polarized reflector antenna assembly with transceivers mounted proximate the backside of the reflector. The internal signal surface of the WO 2007/088183 OMT includes an intricate projecting island septum polarizer feature that may be difficult to cost effectively machine with precision due to OMT element sectioning aligned normal to the signal path. Because the OMT is also the feed hub of the reflector antenna, it may be difficult to harmonize components between various reflector antenna configurations and/or apply alternative OMT configurations to existing installations, for example in a field conversion/upgrade of existing reflector antenna assemblies from single to dual polarized operation.
90 degree signal path changes within the OMT are required to align the OMT output ports at the transceiver side of the OMT/feed hub with the longitudinal axis of the reflector antenna. WO 2007/088184 interconnecting waveguide elements between the OMT and the input ports of the transceivers must therefore have additional 90 degree bends to mate with the transceivers in a close coupling configuration normal to the longitudinal axis of the reflector antenna. Each additional 90 degree signal path change complicates manufacture, extends the overall signal path and introduces an additional opportunity for IPI and/or depolarization degradation of the signals.
Microwave operating frequencies extend over a wide frequency range, generally between 6 and 42 GHz. Prior reflector antenna solutions are typically designed only for narrow portions of this frequency range, requiring an entire redesign, tooling, manufacture and inventory of entirely different reflector antenna assemblies to satisfy market needs.
Competition in the reflector antenna market has focused attention on improving electrical performance and minimizing overall manufacturing, inventory, distribution, installation and maintenance costs. Therefore, it is an object of the invention to provide a dual polarized reflector antenna arrangement that overcomes deficiencies in the prior art.